In other words, if you dont use On Error then this is the behavior you will see. When an error occurs, vba stops on the line with the error and displays the error message. The application requires user intervention with the code before it can continue. This could be fixing the error or restarting the application. In this scenario no error handling takes place. Lets look at an example. In the following code, we have not used any On Error line so vba will use the On Error Goto 0 behavior by default. Sub UsingDefault dim x As Long, y as Long x 6 y 6 / 0 x 7 End Sub The second assignment line results in a divide by zero error.
Vba on Error Statement handling Errors in Excel Macros
Unexpected errors use vba error handling statements to handle savita them. The vba on Error statement is used for error handling. This statement performs some action when an error occurs during runtime. There are four different ways to use this statement On Error Goto 0 the code stops at the line essay with the error and displays a message. On Error Resume next the code moves to next line. No error message is displayed. On Error Goto label the code moves to a specific line or label. This is the one we use for error handling. On Error Goto -1 clears the current error. Lets look at each of these statements in turn. On Error Goto 0 This is the default behavior of vba.
Let me explain this with an example. Imagine you have an application that requires you to add the values in the variables a and b result a b Lets say you mistakenly use an asterisk instead of the plus sign result a * b This is not a vba error. Your code syntax is perfectly legal. However, from your requirements point of view it is an error. These errors literature cannot be dealt with using error handling as they obviously wont generate any error. You can deal with these errors using Unit Testing and Assertions. I have an in-depth post about using vba assertions see how to make your Code bulletProof. As we have seen there are two ways to treat runtime errors Expected errors write specific code to handle them.
If the file does not exist then a user friendly message is displayed and the code exits the sub. Sub OpenFile dim sFile As String slogan sFile "C:docsdata. Xlsx" ' mother use dir to check if file exists If Dir(sFile) " Then ' if file does not exist display message MsgBox "Could not find the file " sFile Exit Sub End If ' code will only reach here if file exists Workbooks. Open sFile End Sub When we think an error is likely to occur at some point, it is good practice to add code to handle the situation. We normally refer to these errors as expected errors. If we dont have specific code to handle an error it is considered an unexpected error. We use the vba error handling statements to handle the unexpected errors. Runtime Errors that are not vba errors Before we look at the vba handling there is one type of error we must mention. Some runtime errors are not considered errors by vba but only by the user.
Runtime Errors Runtime errors occur when your application is running. They are normally outside of your control but can be caused by errors in your code. For example, imagine your application reads from an external workbook. If this file gets deleted then vba will display an error when your code tries to open. Other examples of runtime errors are a database not being available the user entering invalid data a cell containing text instead of a number As we have seen, the purpose of error handling is to deal with runtime errors when they occur. Expected Versus Unexpected Errors When we think a runtime error could occur we put code in place to handle. For example, we would normally put code in place to deal with a file not being found. The following code checks if the file exists before it tries to open.
Vba error Handling - a complete guide - excel Macro mastery
If there are no errors left and you run Debug- compile, it may appear the that nothing happened. However, compile will be grayed out in the debug menu. This means your blue application has no compilation errors at the current time. Debug- compile Error Summary debug- compile finds compilation(project wide) errors. It will also find syntax errors. It finds one error each time you use.
When there are no compilation errors left the compile option will appear grayed out in the menu. Debug- compile Usage you should always use debug- compile before you run your code. This ensures that your code has no compilation errors when you run. If you do not run Debug- compile then vba may find compile errors when it runs. These should not be confused with Runtime errors.
When you type a line and press return, vba will evaluate the syntax and if it is not correct it will display an error message. For example if you type, if and forget the. Then keyword, vba will display the following error message some examples of syntax errors are ' then is missing If a b ' equals is missing after i for i 2 to 7 ' missing right parenthesis b left abcd 1 Syntax errors relate. They occur when the syntax of one line is incorrect. Note: you can turn off the syntax error dialog by going to tools- Options and checking off Auto syntax Check. The line will still appear red if there is an error but the dialog will not appear.
Compilation Errors Compilation errors occur over more than one line. The syntax is correct on a single line but is incorrect when all the project code is taken into account. Examples of compilation errors are: If statement without corresponding End If statement For without Next Select without End Select Calling a sub or Function that does not exist Calling a sub or Function with the wrong parameters giving a sub or Function the same name. Using Debug- compile to find compilation errors, we use debug- compile vba project from the visual Basic menu. When you select Debug- compile, vba displays the first error it comes across. When this error is fixed, you can run Compile again and vba will then find the next error. Debug- compile will also include syntax errors in its search which is very useful.
Vba - add On Error Resume next to my working code
This is where the vba error handling statement comes into play. They allow our application to deal gracefully with any errors we werent expecting. To understand error handling we must first short understand the different types of errors in vba. There are three types of errors in vba. Syntax, compilation, runtime, we use words error handling to deal with runtime errors. Lets have a look at each of these error types so that it is clear what a runtime error. Syntax Errors, if you have used vba for any length of time you will have seen a syntax error.
Raise, a function that allows you to generate your own error. Error Function, returns the error text from an error number. Error Statement, simulates an error. Error Handling refers to code that is written to handle errors which occur when your application is running. These errors are normally caused by something outside your control like a missing file, database being unavailable, data being invalid etc. If we think an error is likely to occur at some point, it is good practice to write specific code to handle the error if it occurs and deal joint with. For all other errors we use generic code to deal with them.
the error. On Error Resume next. Ignores the error and continues. On Error Goto label, goes to a specific label when an error occurs. This allows us to handle the error. Err Object, when an error occurs the error information is stored here. The number of the error. (Only useful if you need to check a specific error occurred.) scription, contains the error text. Urce, you can populate this when you use Err.
In vbscript the pattern shown above is the only form of exception handling you even have since there are brief no gotos or labels. What's objectionable is arming explicit exception testing at the head of every procedure and ignoring. Trust the force, luke approach to trying to mask coding errors. ms-dos error message circa 1986. This post provides a complete guide to vba error Handing. If you are looking for a quick summary then check out the quick guide table in the first section. If you are looking for a particular topic on vba error Handing then check out the table of contents below(if its not visible click on the post header).
Error Handling in Excel vba - easy Excel Macros
It is perfectly reasonable to use. On Error Resume next to implement local writing structured error handling. This involves testing for an exception and acting on it of course, as well as disarming the mechanism afterward. Example: On Error Resume next, getAttr strFilePath, if Err Then On Error goto 0 'deal with "no file" scenario. Else On Error goto 0 'Open and process the file. That's just a simple example where only one sort of exception is expected. In some cases it is necessary to test mber for specific values and take different actions based on them. The unstructured approach based on goto label can often work as well, but it is hardly superior in most instances.